Physics 2011 JAMB Past Questions - Question 27: A certain far-sighted person cannot see objects closer to the eyes than 50 cm clearly.Determine the power of the converging lens which will enable him to see at 25cm

Correct Answer

B

Explanation

To determine the power of a converging lens that will enable a person to see objects at a closer distance, you can use the lens formula:

\[P = \frac{1}{f}\]

Where:
- P is the power of the lens in diopters (D).
- f is the focal length of the lens in meters (m).

In this case, the person cannot see objects closer to the eyes than 50 cm clearly, and they want to be able to see objects at 25 cm. The focal length of the lens needed to achieve this can be calculated as follows:

\[f = \frac{1}{d}\]

Where:
- d is the desired object distance, which is 25 cm (0.25 m).

Now, let's calculate the focal length of the lens:

\[f = \frac{1}{0.25 \, \text{m}} = 4 \, \text{m}^{-1}\]

Now that you have the focal length, you can calculate the power of the lens using the lens formula:

\[P = \frac{1}{f} = \frac{1}{4 \, \text{m}^{-1}} = 4 \, \text{D}\]

So, the power of the converging lens that will enable the person to see objects at 25 cm is 4 diopters.